Approach for Obtaining Material Mechanical Properties in Local Region of Structure Based on Accurate Analysis of Micro-indentation Test

The hot or cold processing would induce the change and the inhomogeneous of the material mechanical properties in the local processing region of the structure,and it is difficult to obtain the specific mechanical properties in these regions by using the traditional material tensile test.To accurately get actual material mechanical properties in the local region of structure,a micro-indentation test system incorporated by an electronic universal material test device has been established.An indenter displacement sensor and a group of special micro-indenter assemblies are estab-lished.A numerical indentation inversion analysis method by using ABAQUS software is also proposed in this study.Based on the above test system and analysis platform,an approach to obtaining material mechanical properties in the local region of structures is proposed and established.The ball indentation test is performed and combined with the energy method by using various changed mechanical properties of 316L austenitic stainless steel under differ-ent elongations.The investigated results indicate that the material mechanical properties and the micro-indentation morphological changes have evidently relevance.Compared with the tensile test results,the deviations of material mechanical parameters,such as hardness H,the hardening exponent n,the yield strength σy and others are within 5%obtained through the indentation test and the finite element analysis.It provides an effective and convenient method for obtaining the actual material mechanical properties in the local processing region of the structure.

Study of the Thermal Characteristics of a Geomaterial:Case of SavèGranites in the Republic of Benin

This work focuses on the valorization of local materials.The rock that is granite,a material used in construction thanks to its mechanical resistance,is the subject of our study.The granite of the commune of Savè,made it possible to appreciate the thermal behavior of this rock studied with a view to its use as a building material.To this end,a thermal diffusivity measurement test was carried out on this material.Thus,we made samples which were then connected to a data acquisition box via thermocouples.A Python script is used to ensure the collection of temperature values over time.From this thermal diffusivity test carried out on the granite taken from the Savèbreasts,we obtained an average diffusivity a=5.84×10^(-6)m^(2)/s.As a result,the thermal effusivity and the heat capacity of the material were determined having respectively the value 1,351.09 J/(K·m^(2)·s^(1/2))and 547,945.21 J/(m^(3)·K).These different results highlight a thermal characterization of Savègranites as a relevant material in the design and construction of an energy-efficient eco-housing.

Oblique incidence properties of locally resonant sonic materials with resonance and Bragg scattering effects

A locally resonant sonic material （LRSM） is an elastic matrix containing a periodic arrangement of identical local resonators （LRs）, which can reflect strongly near their natural frequencies, where the wavelength in the matrix is still much larger than the structural periodicity. Due to the periodic arrangement, an LRSM can also display a Bragg scattering effect, which is a characteristic of phononic crystals. A specific LRSM which possesses both local resonance and Bragg scattering effects is presented. Via the layered-multiple-scattering theory, the complex band structure and the transmittance of such LRSM are discussed in detail. Through the analysis of the refraction behavior at the boundary of the composite, we find that the transmittance performance of an LRSM for oblique incidence depends on the refraction of its boundary and the transmission behaviors of different wave modes inside the composite. As a result, it is better to use some low-speed materials （compared with the speed of waves in surrounding medium） as the LRSM matrix for designing sound blocking materials in underwater applications, since their acoustic properties are more robust to the incident angle. Finally, a gap-coupled LRSM with a broad sub-wavelength transmission gap is studied, whose acoustic performance is insensitive to the angle of incidence.

Localized Optical Waves in Defocusing Regime of Negative-Index Materials

We study optical localized waves on a plane-wave background in negative-index materials governed by the defocusing nonlinear Schr6dinger equation with self-steepening effect. Important characteristics of localized waves, such as the excitations, transitions, propagation stability, and mechanism, are revealed in detail. An intrigu- ing sequential transition that involves the rogue wave, antidark-dark soliton pair, antidark soliton and antidark soliton pair can be triggered as the self-steepening effect attenuates. The corresponding phase diagram is estab- lished in the defocusing regime of negative-index materials. The propagation stability of the localized waves is confirmed numerically. In particular, our results illuminate the transition mechanism by establishing the exact correspondence between the transition and the modulation instability analysis.

Typology of Local Construction Materials from the Adamawa and North-West Regions of Cameroon

This article summarizes the different local construction materials observed in two regions of Cameroon (Adamawa and North-West). These raw materials were mapped and evaluated using various methods of investigation (spatial distribution, estimation of reserves, development of a database compatible with geo-referenced maps). The results obtained show three types of local construction materials (vegetal, pedological and geological) with quantitative estimation or distribution. Vegetal local materials include herbaceous savanna with strong dominance of straw in Adamawa region than the North West region. Pedological local construction materials include lateritic soils (ferruginous or clayey), harplan, sandy clay and sandy clay soil while geological local construction materials include volcanic, plutonic and metamorphic rocks. Many sites of these geological materials are suitable for the rock quarry plant. Adamawa region also contains sedimentary rocks constituted by metamorphic conglomerate and sandstones. Two main types of residential homes are constructed with these local construction materials in these regions of Cameroon. These include huts and houses.

Challenges of the Use of Instructional Materials in Geography Classroom in Secondary School: Nepal

Geography is an optional subject in the secondary schools in Nepal.This paper is an attempt to examine the challenges of using instructional materials in the geography classroom in community secondary schools in Kathmandu district of Bagmati Province.Geography teachers were selected by purposive sampling offering geography as an optional subject in secondary school.The semi structured interview method was used for data collection.The interviews were recorded on an audio recorder and transcribed.After collecting data,analysis of the data was made through the interpretations of the raw data by interpretative method.The results reveal that the challenges of using materials are non-availability of materials,laziness of the teachers,lack of skill and strategies,financial constraint,lack of appropriate materials in textbook,time constraint,lack of support from authority,lack of geography resource room etc.The remedies of the challenges of using materials are the organizing of training and workshop for teachers on how to use instructional materials,provision of funds by the authorities and government,regular supervision,the improvisation of the local materials and the provision of the various instructional materials which are necessary for teaching etc.

STUDY ON DAMAGE BIFURCATION AND INSTABILITY OF ROCK-LIKE MATERIALS

The critical bifurcation orientation and its corresponding hardening modulus for rock-like geomaterials are derived by considering the effect of stiffness degradation and volumetric dilatancy under the assumption of isotropic damage. The dependency of the localized orientation on the degree of damage and initial Poisson＇s ratio of rock is examined and the bifurcation behavior of the uniaxial compression sample under the plane-stress condition is compared with that under plane-strain condition. It is shown that the localization orientation angle intimately depends on both the initial Poisson＇s ratio and degree of damage for the rock sample under the uniaxial compression condition. As the initial Poisson＇s ratio or degree of damage increases, the orientation angle of the plane on which localization tends to be initiated gets to decrease. At the same time, the localization orientation angle of a rock sample under the plane-stress condition is larger than that under the plane-strain condition.

Soil Properties for Earthen Building Construction in Najran City,Saudi Arabia

:Earth is the most common and important building material used in the construction industry,since it is found in almost every country in the world.Modern earthen construction is alive and well,and is spread over an enormous geographical area.This technique utilizes various earthen materials and numerous methods,and features many benefits for both construction in general and buildings in particular.Najran,a city located in the south of Saudi Arabia,is distinguished by its heritage of earthen architecture,which displays many advantages and a marvelous variety of types and exterior designs.Many weaknesses of the material,however,along with a lack of knowledge and rapid development have caused the uplifting and destruction of many of Najran’s mud and heritage buildings during the last few generations.Not all soil types are suitable for every building need.Soil specification is thus very important in order to ensure that the materials used in construction meet all requirements.The main goal of this study was to invistegate the suitability of local soils for the earthen building construction.Thus,available local materials of common quality were taken from local sites in Najran.Laboratory experimentation and testing was then performed to determine the properties of those materials.The results showed that local soil properties are suitable for using in the earthen block construction since they satisified the specifications.The results were then recorded for use in further studies,as well as to explore heritage building and rehabilitation,and to improve modern earthen building materials and techniques.

Earthen-wooden hybrid houses built by the Dai in Dehong Prefecture,South China

The Dai(or Tai)are an indigenous ethnic group distributed across the upper part of Southeast Asia and South China.Whereas the majority of the Dai living on the Southeast Asian mainland build wooden houses on stilts,Dai populations in South China,especially in Dehong Prefecture,are known for the distinctive architectural style of their hybrid earthen–wooden houses,which stems from their enduring social contact and cultural assimilation with Chinese settlers.This paper,which draws on comprehensive feldwork conducted in Dai villages in Dehong Prefecture,explores the Dai’s hybrid earthen–wooden architecture.Specifcally,it examines the development of forms,the relationship between settlement layouts and house plans,as well as building materials,structures and constructions characterising this architecture using data from qualitative surveys,architectural measurements and interviews.The hybrid architecture of the Dehong Dai demonstrates the fusion of two building cultures—earthen and wooden—that has shaped a vernacular architectural identity that is unique to this area.This paper also presents illustrative examples of earthen–wooden houses,thereby contributing to advancing knowledge about this eclectic,hybrid architecture that remains a gap in the academic literature.

High-resolution characterization of hexagonal boron nitride coatings exposed to aqueous and air oxidative environments

Hexagonal boron nitride （h-BN） is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occurrence of galvanic reactions. Nevertheless, this may not be the case when an h-BN-protected material is exposed to aqueous environments. In this work, we analyzed the stability of mono and multilayer h-BN stacks exposed to H202 and atmospheric conditions. Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H202. Multilayer h-BN offered a good degree of protection. Monolayer h-BN was found to be ineffective in an air atmosphere as well. Even a 10-15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration. By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques, we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate. Fortunately, because of the diffusive nature of the process, the oxidized area did not increase with time once a saturated state was reached. This makes multflayer （not monolayer） h-BN a suitable long-term oxidation barrier. Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy. This technique cannot assess the chemical composition of the deeper layers of a material. Hence, the previous reports, which relied on XPS to analyze the passivating properties of h-BN and graphene, may have ignored some important subsurface phenomena. The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.